Decorative laminates are employed for making table tops, desk tops, sink counters and other members. In making members such as sink counters with integral splash board and rounded edges, it is advantageous to use decorative laminates that can be postformed to a desirable curvature. These laminates are sold in a flat form which, upon heating, will become sufficiently flexible, so that it can be postformed using a suitable hot mold, to arcs of radii of less than three-fourths inch (0.3 cm), for a thickness of from about 3/64 to 1/16 inch (0.019 to 0.006 cm).
Most composite decorative postformable laminates will be made of a core or body layer comprising a plurality of sheets of fibrous material impregnated with a flexibilized thermoset resin. On top of this core, a decorated surface comprising a fibrous print sheet material is bonded. This decorative sheet has either a design printed thereon, or pigments dispersed therethrough to provide a solid color decorative print sheet. Suitable postformable laminates of these types are taught by Palazzolo et al in U.S. Pat. No. 3,378,433.
Ordinarily, a separate resin impregnated clear protective overlay sheet, which may contain some abrasive filler particles, such as silica having a Moh's hardness of 7, is employed over the printed design sheet. This overlay provides better abrasion resistance and good surface appearance. The overlay will be clear, the fibers, resin and any silica used having a similar refractive index, so that the pattern of the print sheet can be seen. These filler particles can be added by various methods, such as those taught by Fuerst, in U.S. Pat. No. 3,373,070 and by Treat, in U.S. Pat. No. 3,287,207, where filler is added to the paper in the paper making process, and by Michl, in U.S. Pat. No. 3,135,643, where filler, thermosetting resin and fibers are coated onto a decorative print sheet to form a separate clear protective overlay.
Pigmented decorative sheets having no printed design will ordinarily have good abrasion resistance and not require a protective overlay sheet. However, such sheets, without an overlay sheet are relatively inflexible. In high pressure postforming laminates, the pigmented solid color laminates without a separate, attached overlay sheet surface have not performed well when postformed to relatively small radii. The primary reason for this appears to be that solid color print sheet papers contain a large amount of colored material, such as china clay, titanium dioxide, and various other pigments, that reduce the paper fiber strength required for satisfactory postforming operations.
Meiser, in U.S. Pat. No. 3,730,828, recognized cracking problems in postformable laminates containing patterned and solid color print sheets. He attempted to solve the problem by using unplasticized, low formaldehyde content impregnating resin in a barrier sheet, which was applied to the post-formable substrate. The use of a separate overlay sheet of course solves the problems, but adds significantly to the cost of the product and requires extra processing steps and in some cases delicate handling procedures.
All of these methods: using separate protective overlay sheets or impregnating the overlay, barrier or decorative print sheets with a highly flexible resinous composition, involve extra processing steps, use excessive filler, or filler that is too hard, making the laminate difficult to machine, or are tedious and expensive. And so, a simplified, low cost method is needed to provide flexible, machinable, pigmented, solid color decorative print sheets which can bond to a core, to provide a laminate that can be postformed to arcs of radii of 3/4 (0.3 cm) inch or less without cracking.